1. Field of the Invention
This invention relates to a developing apparatus suitable for use in an image forming apparatus such as a copying apparatus or a printer, and particularly in a full color image forming apparatus, and having a plurality of developing devices.
2. Related Background Art
In a full color image forming apparatus of the electrostatic recording type or the electrophotographic type, it is practised to contain yellow toner, magenta toner, cyan toner and further, black toner in individual developing devices, superpose the developed image by the respective developing devices one upon another and fixate the developed image in mixed colors en bloc.
It is also practised to support these developing devices on a rotatable developing unit, rotate this developing unit and switch the developing devices opposed to an image bearing member.
In each of such developing devices, provision is made of a developing sleeve, a particular gap and an antenna member for detecting the quantity of remaining developer, and the quantity of remaining developer is detected by a variation in the electric capacity between the developing sleeve and the antenna member.
However, if the antenna member is thus provided in the developing device, it will become necessary to provide wiring from the antenna to the apparatus body through the developing unit, and a special slidable contact for detecting the remaining quantity and the wiring itself will become long.
Therefore, the S/N ratio cannot be made great and accurate detection of the remaining quantity will be difficult to accomplish.
Also, the connecting portion between each developing device and a developer supply portion therefor is separated and connected to switch the developing device for developing a latent image on the image bearing member. Therefore, leakage of the developer occurs. Also, to replace the developing device whose life has expired, it has been necessary for a worker having special knowledge to use a special tool to replace or maintain the developing device.